The present invention relates to the field of overcoat materials, and more specifically relates to overcoat materials functioning as relaxation coatings applied to electrode grids.
There are known or proposed systems for electrostatically moving or assisting with the movement of fine particulate materials, such as marking material (e.g., toner) and the like. One such system is described in U.S. patent application Ser. No. 09/163,839.
According to the teachings of the aforementioned application Ser. No. 09/163,839, a grid of small and closely spaced electrodes are connected to a driver circuit such that a phased d.c. travelling electrostatic wave is established along the grid. Charged particulate material is transported by the electrostatic wave in a desired direction, at a desired velocity.
In such a system, it is desirable to provide a planarized surface over which the particulate material may travel. Such a surface eliminates the problem of particulate material becoming trapped between the electrodes. Furthermore, it is desirable to provide a material over the electrodes to provide rapid charge dissipation at a selected time constant. Arcing between electrodes must be prevented. Wear resistance is also a desired attribute of such a layer. Finally, it is important that such a layer be chemically stable. That is, the layer material must not react with the particulate material nor change characteristics in the presence of the operating environment. However, no known material to date has been able to optimize each of these desired attributes.
It is known to encapsulate electronic devices, such as integrated circuits, in protective coatings. Such coatings may provide physical protection from scratches, and a moisture barrier between the devices and the ambient environment. However, such materials are generally not used as top-surface dielectrics. Furthermore, such insulation and passivation layers typically have very high resistivities to avoid possible electrical shorts between covered leads.
Accordingly, there is a need in the art for a coating which provides a planarized surface, has a selected time constant, is wear resistant, and is chemically stable.